1. Field of the Invention
This invention relates to an air motor, more particularly to a pencil typed air turbine motor driven by compressed air for us as a power source of dental surgery air grinder and the like, and further particularly to an air motor capable of thermally insulating the circumferential overheating of an air-motor housing as well as reducing an exhaust air jet noise.
2. Description of the Prior Art
Conventionally in the prior art, as shown in FIG. 4, in an air motor used for a power source of an air grinder and the like, the motor housing (103) is formed by a metallic member which houses a turbine rotor(101) and a cylinder(102) within the housing, the threaded end portion(105) of a small sized valve tube(104) is screwed in the interior at the rear port of motor housing(103) to connect the valve tube(104) with the motor housing(103) integrally so as to communicate air fluidly between compressed air outlet orifices(106) provided in the valve tube(104) and air inlet apertures(107) provided in the cylinder(102).
An air controlling knob(108) is further screwed on the motor housing(103) so as to cover the outer periphery of valve tube(104). The air controlling knob(108) has a double cylinder structure consisting of an inner cylinder(108b) and an outer cylinder(108a), and the end opening portion of the inner cylinder(108b) is inserted rotatably into the inner circumference at the rear opening portion of motor housing(103) by screwing the outer threaded portion of valve tube(104) in the inner threaded portion of inner cylinder(108b).
The air controlling knob(108) has a annular shaped space in its cross-section between the inner cylinder(108b) and the outer cylinder(108a), the annular shaped space consists of an air exhaust passage(110) which discharges the exhaust air backward from air exhaust ports (109) of the cylinder(102), wherein the compressed air supplying rate is controlled by opening or closing an air control valve(111) which is located between the inner cylinder(108b) of the air controlling knob(108) and the valve tube(106) according to the rotative adjustment of air controlling knob(108).
The above conventional motor, however, has such disadvantage that the air motor normally generates a considerable quantity of various heat, which consist of heat such as the air which heats as compression heats in its compressor and air turbine portion according to the hydrodynamic theory, the friction heat of air turbine rotor(101) and its shaft, the heat of power output shaft with chuck(112) and its working instruments such as a drill or grinder and the like during their respective high speed rotation, although their generated heat are cooled down reciprocatingly by various cooling factors such as the high speed air passing through and within the exhausting passage(109) of cylinder(102) after the rotating work of air turbine rotor(101), heat radiation upon all the surface of pipe line lengthened from an air compressor and the like.
According to a field report from users, however, it is recognized that the extent of the cooling is often dependent on the room temperature of the working location. For example, in case of the airmotor being used in such an environment having a comparatively higher room temperature, it is observed that the surface temperature of the airmotor made of the metallic member gradually rises and becomes too hot for the user due to the material properties of airmotor housing(103) made of the metallic member having a high ratio of specific heat and the lower cooling capacity of air blow inside from the high room temperature.
In contrast, when the room temperature is lower, it is reported that the motor housing(103) becomes too cold for the user. From these circumstances in the conventional motor, it is disadvantageous in that the user is compelled to handle the air motor equipment with the temperature fluctuation of air-motor housing(103).
Another disadvantage of the conventional motor is the noise problem due to the high speed exhaust air jet from the air exhaust passages(109)(110) of the housing(103). Reviewing the structure of the conventional type air controlling knob(108), that originally the annular space portion of exhaust air passage(110), which is provided between the inner cylinder(108b) and the outer cylinder(108a) of air controlling knob(108), has a similar structure of a silencer such as the muffler of internal combustion engine as a silencer of exhaust gas jet noise. However, in the actual problem of the conventional motor, the silencer effect is very low because of the lack of muffler space capacity. The reason of the lack is that the diameter of a pencil type air motor should be smaller as much as possible so that the diameter of air controlling knob(108) is also required to meet with the diameter of the motor housing(103) so as to be able to slidably insert the knob(108) into the rear end port of housing(103), thus the annular space portion of exhaust air passage(110) must be restricted according to the restricted diameter of air controlling knob(108). For the above reason, any noise which is the so-called a supersonic wave type noise to be produced by the air flow having too high speed at each noise generating portions such as the air outlet orifices(106), the air inlet apertures (107), an air exhaust passage(109), the air exhaust passage(110), and the like, cannot be avoided. As another noise producing source is caused by the slidably connecting portion formed between the end port of inner cylinder(108b) and the internal circumference of outer cylinder(108a) where the highly compressed air often leaks out partially from the overlapped portion between the inner cylinder(108b) and the outer cylinder(108a). As a further noise source, the high speed rotating turbine rotor(101) produces a supersonic wave type noise together with covibration with the metallic housing body(103) to produce a resonance noise.